Deciphering the Anionic Redox Process in Li-rich Oxysulfide Cathodes for Li-ion Batteries using Neutron PDF

The energy density of conventional Li-ion batteries can be greatly improved by storing charge through the oxidation of anion ions in the cathode materials, like in Li-rich oxides and Li-rich sulfide. However, oxidizing O2- leads to irreversible oxygen gas evolution, voltage fade and sluggish kinetics, while S2- oxidation suffers from the lower redox potential itself. Instead, designing the dual-anion Li-rich oxysulfides, such as Li2FeSO, through combing the energy advantage of oxygen ligand (O2-) with the stability of sulfide ligand (S2-), offers a whole new chemical space to explore high energy density cathode materials. However, in the Li-rich oxysulfide cathodes, the fundamental structure evolution during anion redox remains poorly understood, and whether O2- oxidation contributes to capacity and the nature of oxidized S2- are still under debate. This proposal aims to apply neutron total scattering and pair distribution function (PDF) to study the local atomic structure of the charged Li-rich oxysulfide occurring during S-redox, including the coordination environment evolution of Li/Fe/Mn, any formation of the amorphous/nanostructured phases, and dimer species (eg. S-S dimer, O-O dimer) as localised ‘defect’ states. This study will allow us uncover the anionic redox process in Li-rich oxysulfide and provide the foundation towards exploring the new high-energy battery materials with dual anion ligands.